[cfe-dev] [RFC] Pragma that applies a specified attribute to declarations

[Hal Finkel via cfe-dev]

On 02/13/2017 06:46 PM, Reid Kleckner via cfe-dev wrote:
> Sounds totally reasonable.

I agree, but can you be more specific about how this will work? Does 
this apply only to function declarations or to all declarations? If the 
latter, will the attribute be applied to all relevant things in the 
subject list for the attribute? Will parsing be delayed? I'm wondering 
how this might work with enable_if.

Also, I don't think we should restrict this to declarations because 
applying to definitions would be useful too. For example 
push(__attribute__((target("avx")))) seems useful.

  -Hal

> I prefer '#pragma clang attribute push(...)' to the other one, since 
> it will fit more easily into our pragma handler code.
>
> The infrastructure for managing pragma stacks that apply attributes to 
> decls should be in decent shape at this point after adding all the 
> stack-based MS pragmas. If it isn't, we should refactor things more, 
> since this is a pretty common pattern.
>
> On Mon, Feb 13, 2017 at 4:24 PM, Alex L via cfe-dev 
> <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>
>     Hi,
>
>     I would like to propose a new Clang pragma that would apply a
>     specified attribute to some specific declarations in a source
>     file. Initially the pragma would only work with annotation-like
>     attributes that explicitly opt-in into allowing this pragma. This
>     will ensure that this pragma can avoid conflicts with other
>     pragmas that apply attributes like "#pragma clang optimize off",
>     etc. The set of declarations that receive the attribute would be
>     attribute-specific.
>
>     I would like to propose the following syntax:
>
>         #pragma clang attribute push(annotate("important")) // or
>     maybe push(__attribute__(annotate("important")))?
>
>         void foo(); // This function will now have the
>     annotate("important") attribute.
>
>         #pragma clang attribute pop
>
>     We would like to use this pragma to apply the new
>     'external_source_attribute' (https://reviews.llvm.org/D29819
>     <https://reviews.llvm.org/D29819>) to all of the declarations in
>     an Objective-C header file that was auto-generated by the Swift
>     compiler without adding additional attribute/macro to each
>     declaration.
>
>     Do you have any thoughts / suggestions about this proposal?
>
>     Cheers,
>     Alex
>
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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